Large vehicles which have a plurality of wheel shafts and are intended for heavy haulage and/or operation in difficult terrain are often provided with drive on two or more of their wheel shafts.
However, vehicles with drive on more wheel shafts tend to have higher fuel consumption than vehicles with drive on fewer shafts even when used in conditions where the extra powered shafts are not necessary for the vehicle's propulsion. This higher fuel consumption is due mainly to increased friction losses in the relating gear devices for power transmission to the various drive shafts.
There are therefore various systems on the market which uncouple the drive of one or more wheel shafts when they are not needed, with the object of reducing the vehicle's fuel consumption.
A system for uncoupling of a wheel shaft drive is described in U.S. Pat. No. 4,046,210 and comprises an uncoupling device placed in the drive shaft gear. However, the available space in the drive shaft gear is very limited in that many different components have to be accommodated therein. Applying that solution on heavy vehicles whose drive shafts and uncoupling devices are subject to great forces means that accommodating in the available space an uncoupling device capable of transmitting such great loads is very complicated.
Another system for uncoupling of wheel shaft drive described in US Patent Publication 2006/0272866 A1 has an uncoupling device placed close to the output shaft from a drive shaft gear. The device comprises an extra shaft placed between the ordinary drive shaft and the power train components which are coupled to the drive shaft. However, that solution with the extra drive shaft means that the uncoupling device occupies considerable axial space, increasing the axial length of the drive shaft gear.
There is therefore a need for a device for uncoupling a vehicle's wheel shaft drive which occupies only a limited amount of space and is capable of transmitting large torques.